Generally, your doctor orders an ultrasound to determine the gestational age of your baby when there’s a history of irregular periods, when the date of your LMP is uncertain, or when conception occurred despite oral contraceptive use.Īn ultrasound allows your doctor to measure the crown-rump length (CRL) - the length of the fetus from one end to the other.ĭuring the first trimester, this measurement provides the most accurate estimation for the age of the baby. Your doctor may change your due date if your fetus is significantly smaller or larger than the average fetus at your particular stage of pregnancy. What does it mean if my doctor changes my due date? Some pregnancy wheels may allow you to enter the date of conception - which occurs within 72 hours of ovulation - instead of the date of your LMP.
When you line up that date with the indicator, the wheel displays your due date. The first step is locating the date of your LMP on the wheel. It’s very easy to estimate your due date if you have access to a pregnancy wheel. This is the method that most doctors use. The other way to calculate your due date is to use a pregnancy wheel. In this example, the due date would be August 8, 2018. Change the year, if necessary (to the year 2018, in this case).Subtract three months (August 8, 2017).Naegele’s rule involves a simple calculation: Add seven days to the first day of your LMP and then subtract three months.įor example, if your LMP was November 1, 2017: First, calculate current gestation using one of the other methods, then go to this section and choose a gestational age.If you have regular 28-day menstrual cycles, there are two ways to calculate your due date. First, calculate current gestation using one of the other methods, then go to this section and choose past or future date.ĭate at future or past gestation: Use to calculate the date at a specific gestation (enter in weeks). Gestation at a future or past date: Use to calculate gestation in the future or past. This calculates the current gestational age and gives an estimated date of LMP.Ĭonception date: If conception is known (eg, date of insemination, ovulation or egg retrieval), then the due date can be calculated by adding 266 days. Ultrasound due date: If a due date has been calculated from an ultrasound in the first trimester, the reverse calculation method is preferred.
Last menstrual period (LMP): The LMP calculation uses the standard method of the first day of your last menstrual period plus 280 days to calculate the due date. This calculator allows you to calculate the following: Use the drop-down menu to calculate your due date or current week of pregnancy.